624 
PLATING. 
fource of a Team by extenfion 5 and a larger cavity would 
have the effeft of making hollow places in the fubftance 
of the fheet, which frequently peal oft’ with the filver after 
plating. 
The proper heat of the metals, and the temperature of 
the mould when the metal is poured, are of great import¬ 
ance, as far as regards the foundnefs of the ingot. When 
the metal is too cold, and its liquidity of courle imperfedf, 
the impurities cannot freely afcend, which caufes imper¬ 
fection in its fubftance. The fame effeft may take place 
from the moulds being cold ; this, with the great conduc¬ 
ing power of the metal mould, rapidly robs the metal of 
its caloric, and leffens its liquidity. The proper heat for 
the moulds is fomething fitort of burning the fat with 
which they are greafed on the interior furface. The pre¬ 
fence of fat which contains hydrogen has a happy efteft 
in preventing the furface being rough. Its prefence is 
therefore effential, and hence the moulds fhould never 
be fo hot as to deftroy it. On the other hand, the metal 
fhould not be too hot, as in this cafe it remains longer in 
the liquid ftate than is proper: this has the effeC of al¬ 
lowing the metal to affume a more complete cryftalline 
arrangement than under ordinary circumftances. When 
an ingot under fuch circumftances is broken, the cryftals 
are very diftinC. The fheet .rolled from an ingot fo caft, 
will be found to exhibit on* its furface very thin loofe 
pieces, which peel off. This is frequently a fource of 
great mifchief to the manufacturer. After the pieces are 
plated and rolled, this laft inconvenience is frequently fo 
great, as to render the whole fheet ufelefs, except to work 
over again. 
When the metal has become folid in the mould, the 
wedges which keep the two halves of the mould together 
are flackened, to prevent the ingot from breaking, by its 
contraction, during cooling. When it is taken from the 
mould, its furface ought to be fmooth and metallic. Its 
fraCture fhould exhibit a rough uniform cryftallization, in 
which the cryftals prefent fmall furfaces. If the cryftals 
appear diftinCt, with large faces, the metal will be fhelly 
when rolled. For the ordinary kind of work thefe ingots 
are generally cut in two in the middle, being more con¬ 
venient for plating than longer pieces. 
The next procefs is to drefs the face of the ingot for 
the purpofe of receiving the filver, on one or both fides, 
as it may be intended to be fiugle or double plated. This 
is effeCied by filing, which is continued till the furface 
becomes entirely free from the lead blemifh. This is fo 
important, that the naked eye fnould not be depended 
upon. A very fmall hole in the ingot would become a 
furface on rolling, and the filver would come off in that 
part. The furface of the copper fhould, therefore, be 
minutely examined by' a magnifier before the filver is laid 
on. The thicknefs of the filver to be laid on the copper 
will be beft known, when it is underftood, that the filver, 
in fingle plated metal, or that plated on one fide only, is 
from 8 to 10 pennyweights to the pound troy of cop¬ 
per; and, of courfe, double that quantity when plated 
on both fides. If the ingot of copper be thick, the 
filver plate to be laid upon it, at eight pennyweights to 
the pound, will be -jL of an inch, and a fquare inch of it 
will weigh about 90 grains. When the plate of filver is 
cut to a little lefs than the fize of the copper furface, 
made flat, and fcraped perfe£fly clean, the copper furface 
being equally clean, they are laid together, and the filver 
plate is tied down with wire. A little of a faturated fo- 
lution of borax is now infinuated under the edge of the 
filver plate on every fide : this fufes at a low red heat, and 
prevents the oxygen of the atmofphere from affe&ing the 
furface of the copper, which would prevent the adherence 
of the filver. In this ftate the ingot is brought to the 
plating-furnace. 
This furnace has an iron door; and there is a grate on 
a level with the bottom of the door. The fuel confifts of 
cokes. The ingot is laid upon the bare cokes, and the 
door flint. When it has acquired nearly a proper degree 
of heat, the plater applies to the hole in the door to 
obferve the proper point when the procefs is finifhed. 
When the filver and copper are uniting, the furface of 
the former begins to be rivetted, and this is the fign to 
remove the ingot from the fire as quickly as poftible. If it 
were allowed to ftop longer, the filver would become 
alloyed with the copper, and completely fpoiled. In 
this procefs, the filver is, in faff, foldered to the copper, 
although no folder is exprefsly employed. It is well 
known to chemifts, that an alloy of filver and copper, as 
well as many other alloys, is more fufible than either of 
the fimple metals. From what takes place in the above 
procefs, it will be eafily inferred, that a portion of filver 
and copper unite at contiguous furfaces, which, fufing be¬ 
fore the filver or the copper, unite the filver with the cop¬ 
per. The ingot, being now plated, is made perfectly 
clean, and is ready to be rolled. The firft rollers em¬ 
ployed for plated metal are of caft-iron, fimilar in fize 
and conftruflion to thofe employed for fheet-iron and 
flieet-copper. The metal is rolled cold, and annealed 
from time to time. When it has gone through the rol¬ 
lers a certain number of times, it acquires fuch a degree 
of hardnels, that the rollers have not much effeff upon 
it | and, if the rolling were continued, the metal would 
crack. To remedy this evil, the metal is taken to a re¬ 
verberatory furnace. It is laid upon a hearth of brick or 
fire-ftone, and the flame of coal made to pafs over it. 
The heat, however, is not intenfe, fince the metal is re¬ 
quired to be flowly heated to a dull red. It,may now be 
cooled in the quickeft way pofilble to fave time, as quench¬ 
ing in water does not affeff it, as is the cafe with fteel. 
It now paffes through the rollers, as before, till it be¬ 
comes hard ; and then annealed and rolled again, till it is 
reduced fomething fnort of the fize required. This be¬ 
ing done, it is again annealed, and paffed through a pair 
of rollers faced with caft fteel, and finely poliftied. This 
gives the furface great fmoothnefs and truth. It is now 
annealed for the laft time : after this, the flieets are im- 
merfed in hot dilute fulphuric acid, then fcoured with fine 
Calais fand, which fits them for the workmen to fiiape 
into different articles of a fmooth or flat form. 
As for thofe elegant articles which appear with orna¬ 
mental open-work, fuch as bread-bafkets, and trays of 
different kinds; they ufed to be formed by piercing the 
fubftance with punches of different ftiapes by means of a 
fcrew-prefs called a fly. But this fpecies of work is now 
become obfolete, in confequence of the invention of pla¬ 
ted wire. The articles are now formed by the varied in- 
terfedlions of wires, which give great lightnefs and ele¬ 
gance, with lefs wafte and more expedition. The work¬ 
men employed in this department are ftill, however, 
called by the old name of pierce-workers. 
The pieces of metal to be plated for the purpofe of 
making wire, are forged out of bar-copper unalloyed. 
Thefe pieces are of a cylindrical ftiape, and about inch 
in diameter. The true cylindrical fhape is given to the 
copper by wire-drawing: it is then made perfe&ly clean 
and metallic by fcraping. The filver to be laid upon it is 
much thinner iu proportion to the copper than was 
ftated in the flieet-metal. The filver is firft formed into 
a tube, one edge projecting a little over the other. A cop¬ 
per cylinder, a little lefs in diameter than the tube, and io 
much longer as to admit one end of it being faftened 
into a hole, is now heated red-hot, and faftened by one 
end in the hole. The tube is now flipped upon it, with 
the Team upwards. A flat fteel burnifher, with rounded 
poliftied edges, and a handle at each end, is now rubbed 
brifkly back ward and forward upon the overlapped edges 
of filver, at the fame time ufing coniiderable prelfure. 
By this means the two furfaces are completely welded 
together, fo that it would be difficult to find where the 
union had taken place. 
The cylinder of copper intended to be plated, is now 
made perfectly clean, the inftde of the filver tube being 
the fame. It is now put upon the cylinder, which is 
about 
